Fluid bed processes for the production of vinyl acetate from ethylene, acetic acid and an oxygen-containing gas in the presence of a fluid bed catalyst are known from, for example, EP-A-0685449, EP-A-0685451 and EP-A-0672453.
EP-A-0685449 discloses a process for manufacturing vinyl acetate in a fluid bed reactor comprising feeding ethylene and acetic acid into the fluid bed reactor through one or more inlets, feeding an oxygen-containing gas into the fluid bed reactor through at least one further inlet, co-joining the oxygen-containing gas, ethylene and acetic acid in the fluid bed reactor while in contact with a fluid bed catalyst material to enable the ethylene, acetic acid and oxygen to react to produce vinyl acetate and recovering the vinyl acetate from the fluid bed reactor.
The manufacture of vinyl acetate from ethylene, acetic acid and oxygen is an exothermic reaction and it is necessary to provide means to cool the fluidised bed reactor heat liberated. Failure to do so could lead to loss of temperature control of the reactor and eventually thermal runaway. In addition to the safety implication of thermal runaway there is the probability of catalyst damage/deactivation as a result of the high temperatures involved.
One means of cooling the system is to inject a liquid into the reaction wherein the liquid is introduced into the reactor for the purpose of removing heat therefrom by evaporation of the liquid.
Water may be used for this purpose, because water has a relatively high latent heat of evaporation. The introduction of water for this purpose, whilst effectively cooling the reaction, however, has surprisingly been found to adversely affect the selectivity to vinyl acetate product. Alternatively, the liquid acetic acid may be used to cool the system. EP-A-0847982 discloses the introduction of recycled acetic acid for this purpose. EP-A-0847982 further states that water may be present in the recycle stream as a by-product of the reaction. In practice, it is very difficult and practically inconvenient to remove all water from the acid recycle stream.